Interpretive Summary: Interpretative Summary: Disposal of saline drainage water is a major problem for irrigated agriculture in arid and semi-arid areas throughout the world. In the past subsurface drainage from irrigated agriculture was unrestricted and often resulted in significant negative environmental impacts. Irrigated agriculture has developed best management practices to minimize its impact on the environment and this paper describes a set of best management practices that were developed for managing drainage systems in arid irrigated areas to also minimize environmental impacts. A set of 6 principles are described that were used in the development. A procedure is described to guide the user through the selection of BMP criteria applicable for the site and then the appropriate management. A case study is provided for the application of the methodology to vineyard in the Murrumbidgee Irrigation Area in Australia.

Technical Abstract:
Drainage water disposal is the one of the largest problems facing irrigated agriculture in arid and semi-arid areas of the world. This effluent contains salt, toxic elements, pesticides, and fertilizers and thus represents a pollution source that contaminates the receiving water body. Some of these conditions are also a problem when drainage is applied to rainfed agriculture, especially where large salinised areas are to be reclaimed. This presents challenges in drainage disposal to avoid deleterious effects on downstream water quality. A review of subsurface drainage in Australia has shown that many systems drain excessive volumes of water, potentially reducing irrigation water use efficiency, and remove considerably more salt than applied in the irrigation water, indicating a mining of stored geologic salt. In the rainfed condition it will also be critical to minimize the mobilization of salt from the soil profile below the rootzone, thus minimizing salt disposal problems.
Best management practices (BMP's) have been developed for irrigated agriculture to address many environmental issues, however, prior to this time there were no BMP's developed for managing subsurface drainage to reduce salt loads in the drainage waters. This paper presents BMP's that were developed for designing and managing subsurface drainage systems used in arid and semi-arid irrigated areas. An example is given of the application of these BMP's to a vineyard in the Murrumbidgee Irrigation Area. This example shows the changes in design, the management structures installed and the effects of these changes on drainage volumes and salt loads.
The authors believe that these best management practices can also be adapted to drainage for rainfed conditions. The principles outlined are broadly applicable to rainfed situations and can be taken as a starting point for subsurface drainage planning, design and management.